It is known to color a surface of a glass substrate by coating a mixture of a glass powder and a colorant on the surface of the glass and then baking the mixture. This method has the advantage that the colorant can be readily coated upon the glass surface, facilitating design using the colorant. However, light may be scattered at a molten boundary of the glass powder so that parallel transmittance of light may be reduced to 80% or less.
To overcome the above problem, different methods have been devised. One of these methods is referred to as an ion exchange method. With this method, an inorganic salt containing Ag or Cu is coated upon the glass surface and then baked. Oxides deposited on the surface of the glass are removed. Generally, this method has the drawback that there may be poor selection capability since the ultrafine particles may not be easy to form for all elements.
It is also known to apply a dyed polymeric film on the glass surface. This method facilitates multiple tone selection and pattern formation. However, the resulting film may not have the desired durability.
It is also known to prepare a metal film paper that is deposited on a glass surface by a sputtering process. The desired film strength may not be realized using the sputtering process. Further, tone and pattern formation may be restricted. Additionally, the apparatus conventionally used to perform the sputtering process are often large. Still further, this type of apparatus may not be suitable for high volume mass production.
It is also known to form a metal oxide film on a glass substrate by baking an organic metal compound in atmospheric air. It may be difficult to form a pattern using this method.
It is also known to color a starting material for the glass. This method may also have the drawback that it is difficult to form a pattern.
In glass coloration, design properties are important. Facilitated tone and pattern formation is one important goal of those involved in the glass coloration field. Recent studies have reported glass colorants capable of producing various tones by fixing a gold colloid with a metal oxide. Pattern formation is carried out using screen printing. This overcomes a number of the problems in the prior art methods and is said to allow production of glass with excellent design characteristics.
However, since coloration is carried out by plasmon resonance absorption of gold colloids, yellow colors may not be developed effectively. Further, the desired variation in tone may not be possible. More particularly, when only gold is used for fine particles in the colorant, while transparent tones such as blue, purple, pink, grey, and green can be produced, the green may be heavily tinted with blue. Grey may also be tinted blue. It is possible that only a strongly reddish tone may be obtainable. A yellow color cannot be formed. Only the tone of a half mirror-like type metallic gloss can be provided for the reflection color, with the chemical resistance being potentially insufficient.